Neuronal Communication 2

Question 1

What are the types of synapses, and how do they differ?

Answer 1

1. Axodendritic synapses: Target dendrites.
2. Axosomatic synapses: Target the cell body; have a larger effect than axodendritic.
3. Axoaxonic synapses: Target the axon; function as a gate to modify the nerve impulse.

Question 2

How do neurons communicate with each other across a synapse?

Answer 2

1. Neuronal communication: Signal travels from dendrites → cell body → axon.
2. Heart muscle cells: Connected by gap junctions for coordinated contraction.
3. Synaptic transmission: Ca²⁺ entry triggers exocytosis of neurotransmitters, which diffuse across the synaptic cleft to activate the postsynaptic cell.
4. Termination of signal: Glial cells have transporters to remove neurotransmitters, or acetylcholinesterase degrades acetylcholine. Passive diffusion or uptake by blood vessels may also occur.

Question 3

What is the role of graded potentials in synaptic communication?

Answer 3

Graded potentials: Local depolarization that diminishes with distance.

• Ripple effect: Like a ripple in water, the signal weakens as it travels along the membrane.

• Action potential: Triggered if depolarization reaches the axon hillock and hits the threshold.

Question 4

What is spatial summation and how does it contribute to action potential generation?

Answer 4

Spatial summation: Multiple synapses fire simultaneously, their signals combine to form a large enough depolarization to reach the threshold and trigger an action potential.

Question 5

What is temporal summation and how does it affect action potential firing?

Answer 5

Temporal summation: Synapses fire at different times but close enough for their signals to overlap, helping reach threshold and trigger an action potential.

Question 6

How do EPSP and IPSP influence action potential firing?

Answer 6

EPSP (Excitatory Postsynaptic Potential): Causes depolarization, making an action potential more likely.

• IPSP (Inhibitory Postsynaptic Potential): Causes hyperpolarization, making an action potential less likely.

• Balance: EPSP and IPSP can cancel each other out if they occur simultaneously.

Question 7

How do K⁺ ions contribute to hyperpolarization in neurons?

Answer 7

K⁺ ions: More concentrated inside the cell than outside. When K⁺ streams out, it causes hyperpolarization of the membrane, making it more negative.

Question 8

What are the different types of receptors at synapses?

Answer 8

Ionotropic receptors: Ligand-activated, fast-acting, open and close quickly to generate postsynaptic potentials.

• EPSP: Na⁺ (depolarization).

• IPSP: Cl⁻, K⁺ (hyperpolarization).

• Metabotropic receptors: Slow-acting, G-protein coupled, resulting in longer-lasting and varied responses.

Question 9

What is the function of inhibitory interneurons between sensory and motor neurons?

Answer 9

Inhibitory interneurons (glycinergic synapse): Prevent the effector from firing, ensuring proper regulation of reflexes and actions.